Radioiodinated dopamine receptor ligand

ABSTRACT

A process for the production of radioiodinated spiperone and certain derivatives thereof, and novel compositions made by the process. The process includes reacting spiperone, thallium trichloride and radioiodine in a sealed reaction vial. The novel compounds are useful for diagnosis of disease states resulting in quantitative changes in dopaminergic receptors.

BACKGROUND

The subject invention relates to radiolabeling dopamine receptorligands. More specifically, the subject invention relates toradioiodination of the dopamine receptor ligand generally known asspiperone, and certain derivatives thereof.

It has been known for some time that spiperone is an antagonist of thedopamine receptor. Further, tritiated spiperone has long been used as aresearch tool for the characterization and quantitation of dopaminereceptors, particularly in the study of certain disease states whichresult in quantitative changes in dopaminergic receptors such asParkinson's and Huntington's diseases, and schizophrenia. Tritium,however, is a weak beta emitter which requires quantitation by liquidscintillation counting. Tritium is also a low specific activity isotope,therefore assays being tritiated spiperone require inconveniently largeamounts of tissue.

Radiobrominated spiperone has also been prepared for use in vitro totest dopamine receptor binding affinity, and in vivo to image dopaminereceptors and to study stimulation of prolactin secretion. Use ofradiobrominated spiperone, however, suffers from the disadvantage ofhaving a very short half-life (57 hours). Also, Br-77 is notcommercially available.

Preparation of non-radioactive iodinated spiperone has also beenreported. However, this non-radioactive iodinated spiperone was reportedto have a twenty-fold decrease in dopamine receptor binding affinity.Also, the process used for this iodination is unknown.

SUMMARY

The subject invention is a process for the production of radioiodinated(¹²³ I, ¹²⁵ I, ¹²⁹ I, ¹³¹ I) spiperone and certain derivatives thereof,and the novel compositions made by the process. These compounds areuseful for diagnosis of disease states which result in quantitativechanges in dopaminergic receptors, and are useful in the detection,isolation and characterization of dopamine receptors. The compoundsexhibit a 100-fold increase in specific activity over the tritiatedcounterparts, and because they are gamma emitters, allow for easierhandling and counting.

DETAILED DESCRIPTION

The subject invention is useful for the preparation of radioiodinatedforms of the 4-phenyl compounds described in U.S. Pat. Nos. 3,155,669;3,155,670 and 3,161,644 issued to Janssen and incorporated herein byreference.

The nomenclature employed below is based on the following nucleus:##STR1##

The compounds to be radioiodinated using the process of the subjectinvention are pharmacologically active substances of the general formula1-oxo-2-R₁ -3-R₂ -4-R₃ -8-R₄ -triaza-spiro(4,5)-decane where R₁ and R₂are preferably hydrogen but can be lower alkyl (one C to three C); R₃ isphenyl (unsubstituted or substituted as detailed below); and R₄ isZ(CH₂)n where n is a positive integer from 0 to 4, and Z is any of avariety of groups as illustrated below and disclosed in theaforementioned U.S. patents issued to Janssen. The following compoundsare representative:

1-oxo-4-phenyl-8-[3-(4-fluorobenzoyl)-propyl]-2,4,8-triaza-spiro(4,5)decane.

1-oxo-4-phenyl-8-(3-benzoylpropyl)-2,4,8-triaza-spiro(4,5)decane

1-oxo-4-phenyl-8-[4-oxo-4-(2-thienyl)-butyl]-2,4,8-triaza-spiro(4,5)decane.

dl-1-oxo-3-methyl-4-phenyl-8-[3-(4-fluorobenzoyl)-propyl]-2,4,8-triaza-spiro(4,5)decane.

1-oxo-4-phenyl-2-acetyl-8-[3-(4-fluorobenzoyl)-propyl]-2,4,8-triaza-spiro(4,5)decanehydrochloride.

1-oxo-4-phenyl-8-[3-(4-chlorobenzoyl)-propyl]-2,4,8-triaza-spiro(4,5)decane.

1-oxo-4-phenyl-8-[2-(1,4-benzodioxanyl)-methyl]-2,4,8-triaza-spiro(4,5)decane

1-oxo-4-phenyl-8-benzyl-2,4,8-triaza-spiro(4,5)decane.

1-oxo-4-phenyl-8-(4-methylbenzyl)-2,4,8-triaza-spiro(4,5)decane.

1-oxo-2-methyl-4-phenyl-8-benzyl-2,4,8-triaza-spiro(4,5)decane.

1-oxo-4-phenyl-8-(3-cyano-3,3-diphenylpropyl)-2,4,8-triaza-spiro(4,5)decane.

1-oxo-2-(hydroxymethyl)-4-phenyl-8-benzyl-2,4,8-triaza-spiro(4,5)decane

1-oxo-4-phenyl-8-(2-methylbenzyl)-2,4,8-triaza-spiro(4,5)decane.

1-oxo-4-phenyl-8-(4-fluorobenzyl)-2,4,8-triaza-spiro(4,5)decane.

1-oxo-2-methyl-4-phenyl-8-[3-(4-fluorobenzoyl)-propyl]-2,4,8-triaza-spiro(4,5)decanehydrochloride.

Most preferred are compositions of the formula ##STR2## where R₃ is##STR3## and X is selected from the group consisting of NH₂, OH, NHR₅ orN(R₆)₂ (where R₅ and R₆ are lower alkyl), N₃, NHCOCH₃ or OCH₃.

Where X in the formula above is N₃, the compounds are useful asphoto-affinity ligands in a well-known technique for irreversiblybinding receptor ligands to their respective receptor sites.

RADIOIODINATION

The radioiodination of spiperone (including derivatives thereof asherein described) is a one step synthesis whereby spiperone (in anystandard solvent such as ethanol), thallium trichloride (dissolved in H₂O, NaH₂ PO₄ buffers etc.) and radioiodine (in solution such as 0.1MNaOH) are allowed to react in a sealed reaction vial. The radioiodine ispreferably carrier-free, but can be less than carrier-free. Any of thewell known radioisotopes of iodine may be used, e.g. I-123, I-125, I-129and I-131.

The reaction is carried out under acidic conditions (pH about 1-6), inan aqueous buffer at about 50°-80° C. for 10-60 minutes.

The resulting compound may then be purified by conventional reversephase HPLC, normal phase HPLC, TLC or by chromatographic methods such asopen column silica gel and alumina. The compound is preferably stored ina solution containing free radical scavengers such as ethanol, propanolor buffers containing proteins.

These novel radioiodinated compounds are radioiodinated on the 4-phenylring in the para position where the ring is unsubstituted, and in themeta position when the ring is substituted in the para position.

Therefore, the radioiodinated counterparts of the compounds above are asdefined where R₃ is ##STR4## where I* is radioiodine and X is selectedfrom the group consisting of OH, NH₂, NHR₅ or N(R₆)₂ (where R₅ and R₆are lower alkyl), N₃, OCH₃, or NHCOCH₃.

The following example illustrates the preferred embodiment of theinvention.

EXAMPLE

This example illustrates the preparation of:

1-oxo-4-(p-iodo-phenyl)-8-[3-(4-fluorobenzoyl)-propyl]-2,4,8-triaza-spiro(4,5)decane,(¹²⁵I)

The following ingredients are added to a sealable reaction vial(variations of ±10% of each reagent are acceptable):

(i) 10 mCi carrier-free ¹²⁵ I (4.5×10⁻⁹ Moles) in 0.1M NaOH.

(ii) spiperone(1-oxo-4-phenyl-8-[3-(4-fluorobenzyl)-propyl]-2,4,8-triazaspiro(4,5)decane) (1.06×10⁻⁷ Moles) in ethanol (42 μl)

(iii) NaH₂ PO₄ (0.9 ml, 0.5M, pH 4.5)

(iv) thallium trichloride (0.006 ml, 9×10⁻⁸ moles in water)

and heated to 65° C. and allowed to react for about 20 minutes. Theresulting solution is purified by HPLC using a reverse phase column suchas a "μ-Bondapack" C-18 from Waters Associates, eluted with anorganic/aqueous buffer (methanol: triethyl ammonium phosphate, 0.01M, pH2.7. Upon analysis by HPLC and TLC it is determined that about 90% oforiginal radioactivity is incorporated. Also, the affinity of the ligandfor the dopamine receptor is maintained at about 3 nanomolar asdetermined in a receptor binding assay using rat striatum tissue.

I claim:
 1. A process for the manufacture of a radioiodinated dopaminereceptor ligand comprising admixing(i) a compound of the formula1-oxo-2-R₁ -3-R₂ -4-R₃ -8-R₄ -triaza spiro(4,5)decane where R₁ and R₂are hydrogen or lower alkyl; R₄ is Z(CH₂)n where n is a positive integerfrom 0 to 4, Z is selected from 3-(4-fluorobenzoyl); 3-benzoyl;4-oxo-4-(2-thienyl); 3-(4-chlorobenzoyl); 2-(1,4-benzodioxanyl); benzyl;4-methyl-benzyl; 3-cyano-3,3-diphenyl; 2-methylbenzyl; and4-fluorobenzyl; and where R₃ is ##STR5## where X is a member of thegroup consisting of OH, NH₂, NHR₅ or N(R₆)₂ (where R₅ and R₆ are loweralkyl), N₃, NHCOCH₃ and OCH₃ ; (ii) thallium tri-chloride; and (iii) asubstantially carrier-free radioisotope of iodine at a temperature andfor a time sufficient to allow formation of the radioiodinated form of(i).
 2. The process of claim 1 where (i) is1-oxo-4-phenyl-8-[3-(4-fluorobenzoyl)-propyl]-2,4,8-triazo-spiro(4,5)decane.3. The process of claim 1 or 2 wherein R₃ is ##STR6##
 4. The process ofclaim 1 or 2 where R₃ is ##STR7##
 5. The process of claim 1 or 2 whereinthe pH of the admixture is between about 1 and
 6. 6. A radioiodinateddopamine receptor ligand produced by the process of claim 1 which hassubstantially all dopamine receptor binding activity retained.
 7. Adopamine receptor ligand produced by the process of claim 2 which hassubstantially all dopamine receptor binding activity retained.